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Is there a "quick and dirty" way to approximately calculate how many calories a dish will absorb from the oils used to cook it's ingredients (Rather than oil used as an ingredient itself)?

Something that can be used to give a rough estimate that regardless that's "close enough" irrespective of the type of oil or the ingredient.

For example, if I fry an onion in half a teaspoon of olive oil, or an egg in a teaspoon of canola oil, should I include the entire calorific value of the oil, or a percentage of it?

As opposed to oil mixed in as in ingredient in batter.

This doesn't need to be exact. Just a good rule of thumb.

A good answer will have some basis, or an explanation of the basis, for how it was obtained. For example, it would include a link to a document detailing the calorific loss of oil due to evaporation or other processes during cooking, and an explanation of how this can be averaged out.

A bad answer will be to argue that differences between ingredients and oils make this impossible without an attempt to answer the core question.

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Oils don't boil in your kitchen, because the temperature required for them to burn (i.e., react with oxygen in the air) is far lower than the temperature where they reach a gaseous state at ordinary levels of pressure. Search engines won't even readily give you the latter information as a result, since they assume you must be mistaken about how basic chemistry works and actually want to know about the smoke point. (Or worse, they'll turn up AI-generated nonsense.) But I was able to find some citations that generally put culinary oil boiling points in the range of 300 degrees Celsius (around 570 degrees Fahrenheit) - well above the smoke point of any of them. (In order to actually measure these boiling points directly, you would need to create an oxygen-free environment first.)

When your oil does smoke in the pan, only a tiny amount of it is actually combusted, and of course generally you try to avoid the oil smoking for any extended period. (Back-of-the-envelope calculations available upon request.) Oil can form into tiny droplets as it's heated, but they won't stay suspended in the air for long - that's why you end up with a sticky residue on the range surface. You can see, again, that the volume of that residue is small compared to the volume of oil you put in the pan.

Consequently, the oil that ends up in your food is pretty close to the amount (by mass, if we're being scientific) that was put into the pan, minus the amount that remains in the pan afterwards. There aren't significant chemical changes at ordinary cooking temperatures, nor a means for a significant amount to leave the pan besides entering the food. That is, heating the oil for cooking doesn't cause a meaningful amount of it to burn, therefore it doesn't release a meaningful amount of food energy - just like the food you put in the pan to cook doesn't lose calories from being cooked. (Inside your body, chemical reactions can occur that release the energy from the carbohydrates, fats and proteins in the food. But these processes can occur at a much lower temperature, because they aren't burning - they're decomposition by strong acid and enzymes.)

Your food ends up containing pretty much the remainder of the oil, which has pretty much the same caloric density as it did at the start.

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    "You can see, again, that the volume of that residue is small compared to the volume of oil you put in the pan." -- All I can see is that you haven't seen me cooking.
    – Colombo
    Mar 17 at 20:39
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    @Colombo Fair enough. In that case you would have to account for that. Mar 18 at 14:17
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    I don't think it negates your larger point but the fact that one of the primary functions of a range hood is oil extraction, and the need to clean out the oil trap(s) on a regular basis is pretty solid evidence that the oil doesn't just fall back in the pan from the air.
    – JimmyJames
    Mar 18 at 18:00
  • When I deep fry, I dispose of the used oil in the original container. Because of this, I can estimate that perhaps only about 10% of the frying oil is absorbed into food during cooking. Mar 19 at 0:14
  • @ToddWilcox if the original container is plastic I hope you fully cool it first! Mar 19 at 0:31
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Wellll… not really. Not exactly like you’re asking. But yes, for practical purposes.

Try this: saute a whole eggplant in a reasonable amount of oil (2 tbsp or so) for several minutes, then visually inspect how much oil remains.

Now cube up the eggplant and saute it again.

Now do the same, but with an equivalent quantity of courgette.

What you’ll see is that the rate of oil absorption is determined almost entirely by the ingredients, and by how they’re prepared.

Luckily, though, oil doesn’t evaporate during cooking. A very small amount might escape as an aerosol, but essentially all the oil is either left in the pan or going in your mouth. So if your pan isn’t significantly oily afterwards, the rule of thumb is 100%. But if it is, the answer depends entirely on how much oil is left.

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    Let it cool just a bit before measuring the leftover oil - still slightly warm and it's runnier. and do make sure there's no water in the oil first, or you'll think you're pouring off more than you really are (e.g. after frying mushrooms which release a lot of water)
    – Chris H
    Mar 15 at 22:21
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    @AaarghZombies Yes, that could be your rule of thumb: no oil disappears, all of it either goes into the food or stays in the frying pan.
    – quarague
    Mar 16 at 8:21
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    @AaarghZombies nothing burns off (unless your cooking goes badly wrong). Very little evaporates. A bit spatters. This is well within rounding error but if you wanted to get an idea of how much, use one of those mesh spatter screens over your pan, lifting it slightly to stir, and see how much it catches. I doubt I could measure the difference even on my 0.1g scales
    – Chris H
    Mar 16 at 10:46
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    @AaarghZombies The source for this is a high school chemistry class of the kind that is mandatory for all students.
    – Nobody
    Mar 16 at 17:58
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    @AaarghZombies Pretty much all food oils and fats have a lower smoke point (the temperature at which they start burning) than boiling point (in fact, for most of them any boiling point is only theoretical, because determining it experimentally would require an oxygen-free environment). If you get above the smoke point, you do lose some of the oil to combustion, but you’re only really going to see that if you’re cooking things way too hot, using certain unrefined oils, or using old oils/fats that have started to go rancid. Mar 16 at 19:19
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Airfryer: 7-8g oil per 500g veggies

I have routinely been airfrying about 500g of varying veggies cut in 1x1cm wedges almost every day for like a year by now. In trying to narrow down the optimum amount of oil, I have always weighed the oil I used to toss the veggies in for an even coat. I have narrowed it down to about 7-8g oil per 500g veggies. This is when I have a more-or-less full coating but still next to no oil dripping through the grid in the frying basket.

Needless to say this metric will vary wildly between other kinds of dishes, but maybe you find it useful as a ballpark anyway.

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I don't think it is going to be possible to have a general rule of thumb, as the calories added from cooking oil will vary greatly with the preparation of the ingredients and the method of cooking.

The oil in your frying pan ends up in multiple places; in approximate quantity order:

  1. Absorbed into the food
  2. Left behind in the pan
  3. Congealed and caramelized into goo in the pan, which you may or may not deglaze into the food
  4. Carbonized into black gunk
  5. Splattered onto your stovetop (and hands, if you're unfortunate.)

Even for something simple like potatoes, consider the oil absorption of pan-roasted potatoes vs. deep-fried French fries vs. hash browns vs. mashed potatoes cooked in the pan with your meat grease.

I might outsource this information gathering -- look in a reliable cookbook for similar foods prepared in a similar manner, and look at the nutrition information posted there, which may be based on actual analysis of the prepared food.

(Fair warning -- restaurants are known for making food tasty with large amounts of fat (and salt), and as of 2013, about 20% of restaurant menus significantly underreported fat/calorie counts of the food actually being served, as opposed to the portions made by chefs in test kitchens. If you are preparing fried onions like the ones your favorite chain restaurant serves, the calories listed on the menu may be misleading.)

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